Isotherms, kinetic and thermodynamic studies of methylene blue adsorption on chitosan flakes derived from African giant snail shell

Abstract

In the present study, modeling of 19 adsorption isotherms, 8 kinetic models and thermodynamics of methylene blue (MB) adsorption on chitosan flakes synthesized using Archachatina marginata shell wastes was investigated in a batch mode. The operational parameters’ effects on the MB adsorption were studied. The model parameters were statistically analyzed using 10 error functions. The choices of the best fitted adsorption and kinetic models were based on the comparison of the sum of normalized error (SNE) and two statistical tools of information-based criteria. The 5-p Fritz-Schlüender isotherm best fitted the experimental adsorption data of MB on chitosan flakes based on SNE whereby maximum adsorption capacity, axm q , of 143.6660 mg/g was obtained. The adsorption rate of MB on chitosan flakes was kinetically described by pseudo second-order model at all initial concentrations of MB investigated, with film diffusion being the rate-controlling step and the adsorption process chemisorption-influenced. The calculated thermodynamic parameters, kJ/(mol K), negative 0 G  values revealed that the adsorption of MB onto chitosan flakes was physical, endothermic, spontaneous, energetically favorable and exergonic. The reaction mechanism of the adsorption of MB onto chitosan flakes was proposed taking cognizance of the electrostatic force of attraction between the negatively charged surface of the chitosan (biosorbent) and the positively charged MB. alkaline medium by varying pH values using 0.1 M HCl and 0.1 M measured by a pH meter. The effect of initial concentration of MB solution on the % removal of methylene blue (MB) was investigated by using 10 to 60 mL with a fixed amount of 0.1 g of biosorbent (chitosan) at contact time of 30 min, agitated using a mechanical orbit shaker set at 120 rev/min and ambient temperature of 30  2°C. The impact of contact time was carried out within 4 h durations at a fixed mass of 0.1 g chitosan and room 30  2°C. The thermodynamics study, which is hinged on the effect of variation of in within the ranges of 30 to 90°C at a fixed MJ  regression